1. Field of the Invention
The present invention relates to a ball screw unit with lubrication apparatus, in which the lubricating grease is used for lubrication.
2. Description of the Prior Art
The ball screw unit is essentially composed of a screw nut with coupled bolt and a plurality of rolling balls, wherein the nut and bolt move relatively by rolling the balls therebetween. As the ball screw unit performs the work extremely smooth with high precision, it is widely used by various moving sophisticated machinery requiring precise finishing work or fabrication of semiconductors. In order to operate the ball screw unit efficiently and smoothly, the lubrication of its helical track is very important, and neglecting lubrication of the ball screw unit for a long time will result in aggravating the abrasion of the unit by increased friction between the ball and nut.
To effectively reduce the abrasion of the ball screw unit, the installation of a lubrication system is necessary. There are two typical lubrication systems, the first one is affixing it to the two ends of the nut and applying the lubricant to the bolt surface with an applicator so as to lubricate the helical track; the second one is using the scrapers made of an oil contained material to install it at the two sides of the nut so as to contact directly with the bolt thereby lubricating the helical track.
A self lubricating bolt presently in use has an externally attached accessory on the nut, and the interior of the accessory is filled with a duly oil contained felt so as to apply the oil to the helical track when the bolt rotates with respect to the nut. In many electronic and semiconductor industries which require using dust free chambers, the liquid lubricant is a preferable choice for lubrication. However, liquid state lubricant is apt to be granulated so that it is inapplicable to the electronic and semiconductor industries where the absolutely dust free environment is a must.
To solve the aforesaid problem, there is U.S. Pat. No. 5,782,135 which has disclosed a lubrication apparatus. In FIG. 1 of this cited reference, a spacer ball 32 is interposed between two rolling balls 31 to serve as a solid lubrication materials (MOS2, Au, Ag, Pb, PTFE etc.). During operation of the ball screw unit, the dregs produced by the interposing spacer ball 32 being rubbed by two adjacent rolling balls 31 serve as the lubricant for the ball screw unit.
However, lubricating the ball screw unit as such has the following demerits:
1. The spacer ball gradually reduces its size and finally wears down completely, and the remainder of the spacer ball might become an obstacle to clog the normal operation of the ball screw unit.
2. The supply of lubricant only depending on the spacer ball is insignificant which might result in insufficient lubrication to shorten the mechanical lifetime of the ball screw unit.
Although the lubricating grease is applicable to the industries requiring dust free environments, it requires the external power to bring the viscous lubricating grease into the ball screw unit so that the extra high cost and space occupying equipment is a must.
For these defects noticeable on the prior art, an improvement is seriously required.